1. Field of the Invention
Embodiments of the present invention relate to a communication method of a secondary transmitter, for example, a cognitive radio base station, in a multiple-antenna based multiple input multiple output (MIMO) cognitive radio communication system and a beamforming-based MIMO cognitive communication system using a linear array antenna.
2. Description of the Related Art
Currently, great attention is being paid to a cognitive radio communication system that enables a disallowed secondary user to access a spectrum band not used by an existing primary user and thereby perform communication in order to efficiently use a limited spectrum according to an increasing demand for a high speed wireless data service. Here, in the cognitive radio communication system, the secondary user should not interrupt communication of the existing primary user allowed to a predetermined spectrum band.
Accordingly, in the cognitive radio communication system, the secondary user may sense a spectrum band not used by the primary user and select a band advantageous to the secondary user from among spectrum bands not used by the primary user, thereby performing communication.
However, due to an increasing demand for spectrum bands while being closer to an inner city, it may be difficult to discover a spectrum band not being used by the primary user. Accordingly, there is a desire for a method and apparatus that may extend a width of a spectrum band selectable by a secondary user and may also increase the capacity of a cognitive radio communication system by enabling the secondary user to use a spectrum band occupied by the primary user as well as a spectrum band not used by the primary user.